Electron discharge device



1940' A. J. w. M. VAN OVERBEEK 2,225,325

ELECTRON DISCHARGE DEVICE Filed Feb. 9, 1938 INVENTOR. ADRIANUS J.-W. M.VAN OVERBEEK 42mm ATTORNEY.

Patented Dec. 17, 1940 PATENT OFFICE ELECTRON DISCHARGE DEVICE -jAdrianus Johannes Wilhelmus Marie van Over i .beek, Eindhoven,Netherlands, assignor, by mesne assignments, to Radio Corporation ofAmerica, New York, N. Y., a corporation of Delaware Application February9, 1938, Serial No.'18,9,509

' In-the'Netherlands February 13, 1937 -5 Claims. (Cl."250 27 5) A.

This invention: relates toelectron discharge devices of thespace-cha'rgegrid type and havinga cathode, an anodeand one or moreintermediate electrodes amongst which there is a screening oraccelerating electrode.

When using such electron discharge'tubes, more particularly thosedischargetubes which are utilized for the amplification of electricaloscillations, it is of i great advantage that the tube should have aslope which is as high as possible, that is to say that the inclinationofthegrid voltage-anode current characteristic should be as great aspossible. With the use of a discharge tube having an acceleratingelectrode, that is to say of a so-called accelerating grid or spacecharge grid tube, the maximum characteristic slope ofa control gridwhichfollows'such an accelerating grid is decreaseddue to the fact that theelectrons pass around the grid Wires of the accelerating grid, whichresults in an' appreciable decrease of the slope.

:It is the principal object of my invention to provide anelectrondischarge device of the socalled space charge grid type havingimprovements for increasing the transconductance characteristic of thetube.

The applicant has made a number of experiments on this subject and hasfound that an appreciable improvement maybe obtained by utilizing anelectron discharge tube-made according to the present invention; 'Such atube includes a cathode, an anode and'one' or more intermediateelectrodes, one of which is an, accelerating electrode, the latterbeingfconstructed in such man ner that electron beams are formedwhich donot cross or out each other sothat'at each definite pointin front of asubsequent electrodethere occur only electrons witha determinedcomponent of speed perpendicular to the plane of :the subsequentelectrodewhile this electrode or a following electrode is constructedinsuchmanner that the equivalent or resultant-voltage in the plane ofthis electrodeis adapted orproportional to the above mentioned componentwith the result that in a very narrow range of voltages the wholeof theelectron ,streamimpinges, on this electrode or, if the latter isa'grid-like electrode, is allowed to pass.

As the applicant has found by experiments, it is actually possibletogive'the slope a very high value by ensuringthat with an increase of thevoltage of the-control grid suddenly, subs'tan tiall-yall the electronsare -'allowed'-to pass-"In order toattainthis object its notpossible,-how

ever, to utilize vordinary grid constructions flout first of all it isnecessary to-avoid:havingin-front of the controlxgrid a, large number.of electrons .which move ,confusedly. in all directions and ativery.;;difierent speeds ;while, ,in addition, care a;

should .be taken toensurethat the vo1tage:.in the plane of the grid.issuch that in a comparatively small change of voltage all theelectrons aregals lowed 1 to pass ,or are intercepted, that is to saysuch that the voltagegin the electrode surface is adapted tothesgcomponents of the-speed of the electrons in a direction:perpendicular tov the. surface of the electrode. According ;to theinven- ,tion, the, accelerating electrode is constructed to thatend.-in;such manner that the electrons are ,formed into a pluralityofbeams which do not cuteach other whilethe beam-forming elements arearranged ,parallel'to the cathode. According to oneembodiment of thepresent;invention,.use may be madeior this purpose of .an electrodeofsolid sheet material which surroundsthe oath.- ode, andin which only a.few apertures are providedwhich ,ensure that theelectrons proceedingfrom the cathodeare formed into beams. formation of .beamsmay also beeffected, how.- ever, with theaidof constituent parts of the first gridarranged around the cathode, for example the supportingrods of thisgrid. I

The electrons whichemerge from the apertures in the acceleratingelectrode have, however, different speeds and "according to the presentinvention, it is therefore necessary to construct the firstelectrode or,if desired-subsequent electrodes, in a manner sothat actually thevoltagethe plane of the first electrodes that follow the acceleratingelectrode is adapted if this electrode is made more positivesuddenly, topermitnearlyall the electrons to pass orbejintercepted. Accord-- ,ing toone embodiment of the invention,this may .40

be achieved, for example, by'm'aking, if the first electrode, following[after the accelerating electrode-is a grid, the distance between this.grid and the next electrode difierent. at different points along thecircumference of these electrodes, this distance being greatest at thosepoints where;the speed component perpendicular to the surface of thefirst electrode is largest. It isalternatively possible to .utilizeavariablegrid which is,wo un d with. alarge pitch at those ,points wherethe s pee,d component ,of .the electrons perpendicularmoythe gridsurface is small .and with a small pitch at the-points wherethiscomponent, is larger.

i Ihe fundamentaI idea. of ,the.invention;m y doe applied not onlyrto'any-screemgridtube but. also upper half of the tube disclosed, it willbe seen that the electrons are formed intoa beam by tion itself willbest be understood by reference to the following description taken, inconnection with the accompanying drawing in which Figures 1, 2 and 3show top end views of electron discharge devices made according to -myinvention and used in a hexode usefulas a'mixer, an octode useful as aconverter, and a diode respectively. I

Figure 4 is a top end viewof another modification of my invention.

In Figure 1 is shown a tube" illustrating the principle of my invention.An indirectly heated cathode l consists, for example, of acylindricalcathode tube coated with emitting material and has inside. a heatingelement not shown. The electrons proceeding from* the cathode are formedinto'beams' and pass through apertures provided in an acceleratingelectrode 2 in Figure 1 and-2. in Figure 2 into the further portion ofthe discharge tube. In the forms of construction shown in Figures 1and?! a control grid 3 (in Figure 1) and 3' (in Figure 2) is arrangedbetween the cathode and the accelerating electrode while in the tubeshown in Figure 2 an electrode 4 is arranged inside the acceleratingelectrode 2'. In the form of construction shown in Figure 2 theelectrodes 3 and 4 may jointly be utilized as the control grid andtheanode of the local oscillator. Referring to Figure 1 and consideringonly the means of the control grid 3 and the accelerating electrode 2.The electronsin the right half portion of the beam, due to .the fieldresulting from theconstruction of the tube; have a velocityperpendicular to the surface of the screen grid 1, greater than that ofany of the electrons in the beamsinceit is obvious that the angle of theother portions of the beam at the. point where they. strike thescreenelectrode becomes increasingly greater, moving toward the leftportion of the beam. This means that the component of the velocity ofthe electrons perpendicular to grid 1 in the left hand portion of thebeam is less than the component of velocity of the electronsperpendicular to the screen I on the right hand portion of thebeam.Hence it is necessary to space the control grid 6 at the right hand sideso that the effective field at the surface of this electrode isgreaterin the negative sense than the effective field at the surface of thisgrid on, the left hand side of'the grid. With thisarrangement and byproperispacing of .the electrodes, it is possible to produce a tube suchthat substantially all of the electrons are either permitted to passthrough the grid or are returned with a very small chang in voltage ongrid 6. This results in a tube characteristic of the kind desired.

The electron beams emerging from the aperture' in the acceleratingelectrode pass through the tube and finally reach, in the three examplesshowman anode 5 in Figure 1, anode 5' in Figure 2, or anode 51in Figure3. With the formof construction shown in Figure 1' the electrons pass'ontheir way two grids l and Gwhich may be utilized as a control grid anda'screen grid. In order. to attain the eiiect aimed at with the presentinvention, the grid 1 is mounted in such'manner that one side where theelectrons'reach the gridi at a higher speed than on the other side, isremotest from the grid 6, the distance between the two grids decreasingtowards the other side. Another possibility of construction is shown inFigure 2, in which the electrons pass between the accelerating electrodeand l the anode, successively throughgrids 8, 9 and I0. In'order toobtain a correct distribution of electrons, the distance between thegrids 8 and 9 is greater at those points I where the electrons strikethe grid 8 at the highest speed than at the other points of th grid 8.

The electrodes are enclosed in an envelope I I.

In the form of construction according to Figure 3 a correct potentialdistribution is obtained again by giving the anodes a determined shape.

In the embodiment shown in Figure 4 the spacing between the secondcontrol grid I and the screen and anode does not vary but the size ofthe apertures in the second control grid 1 decreases in the direction inwhich the speed components of the electrons perpendicular to the surfaceof the second control grid is the greatest.

In all the figures of the drawing the paths of the electrons arediagrammatically indicated by arrows. i

While I have indicated the preferred embodiments of my inventionof whichI amnow aware,

it will be apparent that my invention is by no means limited to theexactforms illustrated or the use; indicated, but that manyvariations may bemade in the particular structure used and the purpose for which it isemployed without departing from the scope ofmy invention as set forth intheappended claims.

What I claim as new is;

1. An electron discharge device having a cathode for emitting electrons,a control electrode surrounding said cathode and an anode for receivingelectrons-from said cathode, and an accelerating electrode between saidcathode and anerating electrode the spacing between the auxiliaryelectrode and the anode being greatest at the place where the speedcomponent of the electrons perpendicular to the surface of the auxiliaryelectrode is the greatest.

2. An'electron discharge device having a cathode for emitting electronsand surrounded by a control grid, and an anode for receiving saidelectrons, and an accelerating electrode having apertures for, formingthe electrons from the cathode into beams which do not intersect eachother, a second control grid anda screen grid between said anode andfirst control grid, the second control grid having varying sizeapertures, the wide apertures being positioned at those points of thegrid where the speed component of the electrons perpendicular to thesurface of the second control grid is the smallest, and at the positionwhere the speed-component of the electrons is large'rthe apertures aresmaller.

3; An electron discharge device having a cathode for emitting electronsand surrounded by a control grid, and an anode for receiving saidelectrons, and an accelerating electrode having apertures for formingthe electrons emitted by, said cathode into beams, a second controlgridand a screen grid between said anode and first control grid; thescreen grid being spaced at a greater distance from the second controlgrid at those points of the second control grid where the speedcomponent of the electrons perpendicular to the surface of the secondcontrol grid is greater than the speed component of the electronsperpendicular to other portions of the surface of the second controlgrid.

4. An electron discharge device having a cathode for emitting electrons,a control electrode surrounding said cathode and an anode for receivingelectrons from said cathode, and an accelerating electrode between saidcathode and anode having apertures for forming the electrons emitted bythe cathode into beams which have non-intersecting paths, said anodecomprising a plane electrode positioned at an angle to said beams and ascreen grid parallel to the anode, and a second control grid positionedbetween the screen grid and the accelerating electrode, the spacingbetween said second control grid and screen grid being smaller at thosepoints of the second control grid where the speed component of electronsperpendicular to the surface of the second control grid is the smallest,whereby the eifective voltage of the second control grid along thesurface of the second grid is proportional to the component of the speedof the electrons perpendicular to the surface of said second grid.

5. An electron discharge device having a cathode surrounded by a controlelectrode and an accelerating grid for forming electrons emitted by thecathode into beams, and an anode for receiving said beams surroundingsaid cathode, control grid and accelerating electrode and a secondcontrol grid positioned between the cathode and the anode, and a screengrid between said second control grid and said anode, the spacingbetween said screen grid and second control grid being greatest wherethe speed component of the electrons perpendicular to the surface of thesecond control grid is the greatest, and the spacing being smallest atthe portion of the second control grid where the speed component of theelectrons is the smallest.

ANDRIANUS JOHANNES WILHELMUS MARIE VAN OVERBEEK.

